This invention relates to a method and apparatus for controlling the operation of a spark ignited internal combustion engine. The method and apparatus are particularly useful for controlling the operation of a gasoline engine in a motor vehicle.
There are three generally recognized control parameters which are useful for controlling the operation of a spark ignited internal combustion engine of the type used in a motor vehicle. These control parameters include fuel-air ratio, .lambda., mixture volume, Q.sub.L , and ignition timing, more particularly spark advance angle .alpha..sub.z. All of these parameters are generally responsive to the driver's actuation of a gas pedal or other accelerator in the vehicle. The particular condition of these parameters determine the engine output torque and rotational speed. Conventional engines require adjustment, such that, for each setting of the gas pedal, there is an optimum condition for the values of air-fuel ratio, mixture volume, and ignition timing.
Such optimum tuning of all three parameters is difficult, if not impossible, to accomplish for all operating modes of the engine, including idling, partial load and full load, each at various engine speeds. It must also be recognized that the engine must be tuned to achieve high torque output and low fuel consumption, as well as reduced exhaust gas emissions in all operating ranges of the engine. Conventional methods for controlling an engine by coupling all three of these parameters do not achieve the optimum operating performance characteristics and low emission value sought, because it is impossible to separately regulate each of these parameters for optimum operation under the wide range of engine speeds and loads normally encountered by the engine.
In prior U.S. Pat. No. 3,916,840 there is disclosed an internal combustion engine, which includes an auxiliary combustion chamber and wherein there is a division of controls which are activated by the accelerator pedal in two phases. In the first, low range of engine load only regulation of the mixture volume is provided. In a second, higher range of engine load, regulation of mixture air-fuel ratio is provided. Thus there is a separation of mixture ratio and mixture volume controls, and separate variation of these parameters are provided in different load ranges of the engine. This prior art arrangement is limited to an internal combustion engine with an auxiliary combustion chamber, and also provides no specific control of the ignition timing. Control of the spark ignition timing is particularly critical in an internal combustion engine which operates with a high air ratio, that is, a very lean mixture.
U.S. Pat. No. 3,195,529 describes the division of engine control into two load ranges. In this patent it is not clear whether the two control ranges comprise two ranges of engine load, or two ranges of engine speed. In the first of these ranges, including idling or low speed, the throttle is closed and only the spark timing is varied in the direction of advance, to increase engine speed. In the second range, both mixture volume and spark are varied. There is no specific provision for controlling the fuel-air ratio.
It is an object of the present invention to provide a new and improved method and apparatus for controlling the operation of a spark ignited internal combustion engine.
It is a further object to provide such a method and apparatus wherein there is optimal control of three control parameters of the engine, including fuel-air ratio, mixture volume, and ignition timing.
It is a further object of the present invention to provide such a method and apparatus wherein optimum control is realized by the use of a single engine control lever.